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The control delay in distributed control systems may be compensated on-line or off-line depending on the required quality of the output, available computational power of the controller node, time stamping and clock synchronizing facilities etc. Irrespective of the compensation technique, there is an upper bound to the constant or variable control d...
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Citations
... Accuracy of the identified parameters (including the first natural frequency of the plant) is the key to the successful auto-tuning of all control loops. As the position loop of servodrive is an aggregation of nonlinear objects: closed torque loop, mechanical actuator, measuring system and data transmission channels (especially in the control systems with serial data transmission interfaces or with communication networks between the controller and actuator or sensors [3]), identification of the position control loop is still of a great interest today [4][5][6][7][8]. ...
Velocity or Position control loop Bode diagrams of servo drives are commonly used to identify the load inertia and mechanical resonances. Apart from these parameters the Bode diagrams contain the information on the total delay time of the loop. The study considers identification of this delay, the value being highly important for tuning procedures of servo-drives. Total delay time is not easy to calculate analytically as it requires knowing precise values of all particular delays in the loop. In the paper, a robust algorithm for position control loop identification considering possible two-mass structure is pro-posed. Theoretical evaluations are proved by the simulation and experimental results obtained from a several servo drives with different structures of position feedback circuit.
... The control system delay is the summation of the sensor to controller delay, controller calculation delay, and controller to actuator delay. An adaptive sampling scheme has been presented [7] to ensure that the control delay is less than the sampling period in the steady state and uses the maximum tolerable delay at a specified sampling period to ensure stable transformation from one sampling interval to another. Echo state neural networks have been used to improve the shape recognition performance of the sendzimir mill control system [8]. ...
This paper presents a mathematical approach for improving the performance of
a control system by modifying the time delay at certain operating conditions.
This approach converts a continuous time loop into a discrete time loop. The
formula derived is applied successfully to an applicable control system. The
results show that the proposed approach efficiently improves the control system
performance. The relation between the sampling time and the time delay is
obtained. Two different operating conditions are examined to assess the
proposed approach in improving the performance of the control system.
... If not, with any delay compensation technique, the plant will effectively be updated at D and not at h. This has theoretically been verified using a graphical approach in [4] by the same authors and have proposed an adaptive sampling scheme to change the sampling rates at the sensors to ensure D < h. This paper is aimed to practically verify that result using an XY board which is distributed real-time controlled via a Switched Ethernet network. ...
... This can be constant or variable. In the worst case for a variable delay, it can exceed the sampling period (h), giving a lot of detrimental effects as highlighted in [4]. As a solution to this problem, an adaptive sampling scheme is used as described in the next section. ...
... The number of elements in the running average obviously depends on the load profile, which in this case it is 10. As shown in [4], the D comprises a constant overhead and a variable round trip time. The constant overhead in this case is approximately 20µs. ...
With the recent IPv6, Power over Ethernet (PoE) and ro- bust hardware designs, Switched Ethernet technology is currently reaching the status of a complete fieldbus system for harsh factory floor applications. However, the investors still hesitate on its field level operation for time critical ap- plications, due to the non-deterministic delays in the closed world of a switched network. The objective of this paper is to practically prove an adaptive sampling scheme to handle network delays and to highlight the potential of Switched Ethernet in implementing time critical real-time distributed control system applications. Experiments are carried out on a distributed XY board, in which the speed and position control loops on each axis, are closed through a 100Mbps Switched Ethernet network.
Networked control system (NCS) has received considerable attention in the last 15 years. The interest is stimulated by the fast development of communication in computer based control system technologies that offers many benefits in integrating production planning and control. Unfortunately, the network induces imperfections and constraints in control system implementation. One of these limitations which affects the NCS is varying communication delays. The paper shows the occurrence of varying time delays in wireline or wireless network and considers robust control design methods to handle the delay uncertainties.
This paper is focused on controller design for distributed control systems. The performance degradation due to time varying control delays in the loop closed through a network has been addressed by a novel predictor based delay compensation method supported by an adaptive sampling scheme when the control delay exceeds the sampling period. Both continuous and discrete time domains have been considered in the design and a methodology has been derived to transform a continuous time design to discrete time implementation without loosing performance. Since the existing simulation tools support only constant sampling frequencies, a different approach based on a set of differential equations representing the system has also been presented
